Recently, for energy saving, the permanent magnet used in various motors employed in HEV (the hybrid electrical vehicle) or the home appliance is required to be a magnet with high performance. Specially, in order to deal with the working environment at a high temperature, it is required that the magnet should be excellent in heat resistance and has a high coercivity. As a permanent magnet with high performance which has a high coercivity, a permanent magnet formed by adding Dy or Tb in the Nd—Fe—B based magnet is known, however, the use of Dy or Tb is not preferable for resource saving.
Therefore, is order to maximally lower the used amount of Dy or Tb, a magnet is proposed in which only the coercivity at the part affected by large demagnetizing field is increased, and which is the so called structure with the distribution of the coercivity (Patent Document 1).
In order to evaluate a sample in which the coercivity distributed in the magnetic substance is uneven, a device for measuring the coercivity in a microregion of a submillimeter level or less is needed.
So far, a B-H curve tracer or a VSM (vibrating sample magneto-meter) has been used in measuring the magnetic characteristics of the magnetic sample. However, these measurement devices can only measure the average magnetic characteristics of the magnetic sample which is the object to be measured, and cannot measure the distribution of the coercivity, i.e., the coercivity in a microregion.
A method is also considered in which the magnetic sample which is the object to be measured is divided by cutting process or the like and measured by a VSM or the like so that the coercivity in a microregion is measured. However, the inherent coercivity of the magnetic sample cannot be measured due to the damage to the surface layer of the magnetic sample caused by the process.
In order to measure the coercivity in a microregion of a magnetic sample without processing the magnetic sample, a MFM (magnetic force microscopy) is used.
In order to measure the coercivity in a microregion of the sample using a MFM, it is necessary to measure the magnetic sample in a magnetic field. However, as the measuring head is affected by the magnetic field in a magnetic field with a high intensity, the measurement cannot be performed, and it is difficult to evaluate the coercivity in a sample with a high coercivity as obtained by adding Dy or Tb mentioned above.